Wear-resistant, superabrasive compacts are utilized in a variety of mechanical applications. For example, polycrystalline diamond (“PCD”) superabrasive compacts are used in drilling tools (e.g., compacts, cutting elements, gage trimmers, etc.), machining equipment, bearing apparatuses, wire-drawing machinery, and in other mechanical systems.
PDCs have found particular utility as superabrasive cutting elements in rotary drill bits, such as roller cone drill bits and fixed cutter drill bits. A PDC cutting element or cutter typically includes a superabrasive diamond layer or table. The diamond table is formed and bonded to a substrate using an ultra-high pressure, ultra-high temperature (“HPHT”) process. The substrate is often brazed or otherwise joined to an attachment member such as a stud or a cylindrical backing. A stud carrying the PDC may be used as a PDC cutting element when mounted to a rotary drill bit by press-fitting, brazing, or otherwise securing the stud into a receptacle formed in the rotary drill bit. The PDC cutting element may also be brazed directly into a preformed pocket, socket, or other receptacle formed in the rotary drill bit. Generally, a rotary drill bit may include a number of PDC cutting elements affixed to the drill bit body.
Conventional PDCs are normally fabricated by placing a cemented-carbide substrate into a container or cartridge with one or more layers of diamond particles or crystals positioned on a surface of the cemented-carbide substrate. Often, at least two layers of diamond particles are used to tailor the mechanical properties of the resultant PDC. Typically, a number of such cartridges are loaded into a HPHT press. The substrates and the layers of diamond particles are then processed under HPHT conditions in the presence of a catalyst material that causes the diamond particles to bond to one another to form a matrix of bonded diamond grains defining a diamond table. The catalyst material is often a solvent catalyst, such as cobalt, nickel, or iron that is used for facilitating the intergrowth of the diamond particles.
In one conventional approach, a constituent of the cemented-carbide substrate, such as cobalt from a cobalt-cemented tungsten carbide substrate, liquefies and sweeps from the region adjacent to the volume of diamond particles into interstitial regions between the diamond particles during the HPHT process. The cobalt acts as a catalyst to facilitate intergrowth between the diamond particles, which results in formation of bonded diamond grains. Often, a solvent catalyst may be mixed with the diamond particles prior to subjecting the diamond particles and substrate to the HPHT process.
The solvent catalyst dissolves carbon from the diamond particles or portions of the diamond particles that graphitize due to the high temperature being used in the HPHT process. The solubility of the stable diamond phase in the solvent catalyst is lower than that of the metastable graphite under HPHT conditions. As a result of this solubility difference, the undersaturated graphite tends to dissolve into solvent catalyst and the supersaturated diamond tends to deposit onto existing diamond particles to form diamond-to-diamond bonds. Accordingly, diamond grains become mutually bonded to form a matrix of PCD with interstitial regions between the bonded diamond grains being occupied by the solvent catalyst.
When the diamond table is formed from a number of different layers of diamond particles with distinctly different particles size distributions, the resultant HPHT-processed diamond table comprises a number of distinct layers. Each of the layers of diamond has a different average grain size. While layering diamond grain sizes in the diamond table is often performed to improve the mechanical properties of the diamond table, the layering can introduce undesirable stress concentrations between adjacent diamond layers and/or between one of the diamond layers and the substrate. The diamond tables often fail during use by delaminating at the interface between adjacent diamond layers. Moreover, even when the diamond table comprises only a single layer of diamond, the diamond table can often delaminate at the interface between the substrate and the diamond table.